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Daniel Arnold, Esq. April 6, 2011 Denver Water Page 4 of 12 cause of the elevated uranium concentrations in MW -6 and MW -7. Note that the uranium concentrations in these two well begins to steadily increase around the 2006 to 2007 timeframe, which is when the mine pool reached the elevation of the wells and began to impact alluvial groundwater quality. Issues are raised by Cotter on the merits of dewatering of the mine pool, including: • Dewatering will interfere with locating and plugging conduits or seepage pathways. • It will require a large evaporation impoundment and expansion of water treatment facilities. • Large amounts of constituents would be brought to the surface. • It would increase potential exposures to human health and the environment. Any of these issues, alone or in combination, does not preclude maintaining a mine pool elevation below the level of the creek. This will assure that the mine pool is not a source to alluvial groundwater and the creek. Only after the mine pool is drawn down would the impacts of the other sources (waste rock piles and alluvial fill) be realized and quantifiable. It is stated that water quality impacts in the creek begin about 300 feet downstream of where the Illinois Fault intersects the creek and this suggests that the fault may not be responsible for the impacts. This reasoning does not take into account the understanding of groundwater flow and the interaction between groundwater and the creek. Water from the mine is likely to be discharging to the alluvium /fill material along the fault. The alluvial groundwater flow direction where the fault intersects the creek is parallel to the creek and at this location the creek does not gain water from the alluvium. Mine pool water discharging along the fault would flow in line with the creek (southeast) until reaching the constriction point where it discharges into the creek. Therefore, it is not expected that the fault would impact the creek where it intersects, rather some distance downstream where the creek begins to gain water from the alluvium. The issue of background bedrock groundwater quality is discussed. It is stated that wells MW -10 and MW -11 "...were never intended to establish background groundwater quality." Outside of mine - influenced area, background conditions are probably best realized where the Schwartz Trend crosses the creek downstream of the mine between SW -FBRG and SW -ARH. The Schwatrz Trend is comprised of brittle biotite gneiss and quartzite and the EPP states that "...the uranium deposit is essentially limited to the Schwartz Trend rocks." Based on historic surface water quality data from the two sampling locations, uranium concentrations generally decrease across the trend, indicating that mineralize rock within the trend that is in contact with water probably does not liberate significant uranium. Therefore, the background uranium signature associated with the mineralized ore zone may not be as high as believed.